Noninvasive spatiotemporal spinal neuromodulation targeting dorsal roots improves paretic leg motor control during walking in persons with stroke

Individuals post-stroke demonstrate impaired motor control and muscle weakness in the paretic leg interfering their mobility. We aimed to determine whether applying spatiotemporally controlled transcutaneous spinal cord stimulation (tSCS), when combined with constraint force-induced forced use (CIFU), enhances paretic leg motor control during walking in individuals post-stroke. Thirteen individuals with stroke (age: 64.2 ± 7.1 yr old; time post-stroke: 14.1 ± 6.1 yr) were tested in a crossover design under two conditions: active versus sham tSCS during CIFU treadmill walking (tSCS + CIFU vs. sham + CIFU). In both conditions, CIFU treadmill walking was performed with a constraint force applied to the nonparetic leg during the swing phase of gait. For the active condition, tSCS was delivered at L4 during the swing phase (80 Hz) and at S1 during the stance phase (30 Hz) of the paretic leg, filled with a carrier frequency of 9.5 kHz. Spatiotemporal gait parameters, muscle activity, and propulsive force were assessed. Participants showed greater increases in paretic step length and step height in the tSCS + CIFU condition compared with the sham + CIFU condition, whereas showed prolonged paretic stance time in both conditions. The tSCS + CIFU condition also showed significantly less foot path variability of the paretic leg compared with sham + CIFU. Muscle synergy analysis revealed increased muscle weightings in plantarflexion, dorsiflexion, and hip/knee extension synergies of the paretic leg in both conditions. Propulsive force of the paretic leg showed no change in both conditions. In conclusion, applying spatiotemporally controlled tSCS during CIFU treadmill walking may enhance paretic leg motor control in individuals post-stroke.<b>NEW & NOTEWORTHY</b> Applying spatially and temporally controlled transcutaneous spinal cord stimulation, combined with constraint force applied to the nonparetic leg during swing, may induce greater improvements in step length and step height of the paretic leg, and reduced foot path variability in the paretic leg compared with the sham stimulation, combined with targeted constraint force during walking. These findings support the development of targeted spinal cord neuromodulation strategies to enhance paretic leg motor control in individuals post-stroke.